The goals of this grant are to understand the assembly, dynamics, and functions of stress granules in the control of gene expression and how aberrant stress granule formation contributes to neurodegenerative diseases. Stress granules are cytoplasmic granules of mRNAs and proteins that form when translation initiation is limiting and assemble in part by interactions between prion-like domains on RNA binding proteins. Stress granules are of importance for two reasons. First, they sequester mRNAs and mRNA binding proteins and play important roles in modulating gene expression and cellular signaling during stress responses. Second, aberrant stress granule accumulation appears to be a causative event in diseases such as Amyotrophic Lateral Sclerosis (ALS), or Frontotemporal lobar degeneration (FTLD). These diseases can be caused by mutations in RNA binding proteins, such as hnRNPA1, which increase stress granule assembly and promote toxic amyloid formation, or by mutations in the AAA-ATPase VCP, which decrease stress granule clearance by autophagy. Given this importance in both normal stress responses and in pathological conditions, an understanding of both normal and pathological stress granule dynamics is critical. We will take advantage of the powerful approaches in yeast cells to understand fundamental aspects of stress granule dynamics and function. We will also apply our knowledge from yeast to understand how pathogenic mutations affect stress granules in mammalian cells. The specific questions addressed in this proposal are: I) What are the composition, dynamics and affects of stress granules in both normal and pathogenic conditions? II) What are molecular mechanisms connecting stress granule assembly with toxic amyloid formation? III) What are the mechanisms by which stress granules are targeted for autophagy? Completion of these aims will reveal fundamental principles of stress granule dynamics and how aberrant stress granules form and contribute to degenerative diseases, which could facilitate the development of new therapies.